Methods of construction of evacuated glazing

Abstract: A method of forming the edge seal (13) for a thermally insulating glass panel comprising two spaced apart sheets of glass (10,11) enclosing a low pressure space (30) interconnected by a glass solder edge seal (13) and an array of pillars (12), the method characterized in that it includes the steps of (a) preparing first and second sheets of glass (10,11) such that when they are brought together their edges (14,16) are not in registration, and at any point around the periphery of the panel the edge (14) of one of the sheets of glass extends beyond the edge of the other; (b) depositing a strip of solder glass around the periphery of the panel on the extending edges of the glass sheets; (c) heating the panel to melt the solder glass such that it runs between the glass sheets; and (d) cooling the panel to solidify the solder glass.

Description: INTRODUCTION The invention described in this specification concerns an improvement to the design of thermally insulating glass panels. These panels typically comprise two spaced apart sheets of glass enclosing a low pressure space and interconnected by an edge seal and an array of support pillars. The panels are used for glazing, and such thermally insulating windows are generally referred to as evacuated glazing. BACKGROUND Thermally insulating panels are typically constructed by depositing a strip of solder glass around the periphery of the glass sheets, depositing an array of support pillars onto one or other of the sheets of glass, bringing the sheets together or permitting them to move together, heating the panels to melt the solder glass around the periphery so that the two sheets settle onto the pillars, and then cooling the panel to solidify the edge seal. The panel is then evacuated by pumping out through a tube positioned either through one of the glass sheets or through the edge seal, and finally the pump-out tube is melted and sealed off. The invention concerns the edge seal, and in particular a method of constructing a thermally insulating glass panel with a superior edge seal, and a panel incorporating the superior seal. Several conditions must be satisfied in the construction of evacuated glazing. First, it is necessary to produce an hermetic (leak-free) edge seal around the periphery of the panel. Second, in order to prevent the glass sheets from being forced into contact with each other, by the large atmospheric pressure forces acting, it is essential to include an array of support pillars within the glazing. Third, the space between the glass sheets must be evacuated to a high level, and this level of vacuum maintained over the life of the glazing. Fourth, in order to reduce radiative heat flow through the glass, a low emittance coating is applied to the inner surfaces of one or both sheets of glass. One of the methods of forming the edge seal around the periphery of evacuated glazing is to use a low melting point glass (solder glass). In order to manufacture such an edge seal, solder glass is deposited as a liquid slurry onto the surface of one or both of the glass sheets, around the edges. The glass sheets are brought together and the entire assembly is heated to a temperature at which the solder glass melts, wets the surface of the glass sheets, and flows to produce an hermetic seal between the sheets. One of the difficulties is that even at the high temperatures used the solder glass possesses a relatively high viscosity, and it does not flow readily between the glass sheets. If there is too much solder glass in the gap between the sheets, it may not flow out of the gaps sufficiently to allow the upper sheet to settle down onto the pillars during the edge sealing process. This leads to large tensile stresses in the glass sheets near their edges when the vacuum is eventually created. The publication WO 91/02878 describes a thermally insulating glass panel and a method of construction thereof in accordance with the above discussed prior art. The publication US 4,277,275 describes a liquid crystal display panel comprising two spaced-apart glass sheets enclosing a space and interconnected by a glass solder seal. The problems arising from these prior art devices and methods are discussed above. SUMMARY OF THE INVENTION The invention provides a method of forming an edge seal for a thermally insulating glass panel that comprises first and second spaced-apart sheets of glass enclosing a low pressure space interconnected by a glass solder edge seal and an array of pillars. The method comprises the steps of: (a) arranging the array of pillars between the first and second sheets of glass to support and space apart the sheets of glass, and such that their edges are not in registration, and at any point around the periphery of the panel the edge of one of the sheets of glass extends beyond the edge of the other; (b) after step (a), depositing a strip of solder glass around the periphery of the panel on the extending edges of the glass sheets; (c) heating the panel to melt the solder glass such that it runs between the glass sheets; and (d) cooling the panel to solidify the solder glass. In this way solder glass does not intrude between the sheets before it is melted, thereby overcoming the current problem in conventional construction methods. The first and second glass sheets are conveniently prepared by making one slightly smaller than the other. For instance the upper glass sheet may be 5 mm less than the lower on all sides; in other words 10 mm less in each orthogonal direction. The solder glass strip may be deposited on the extending edges such that it bridges the gap between the sheets and contacts the end edge of the other sheet. Another advantage of the method is that the solder glass flows into the gap between the two glass sheets a uniform distance all around the periphery of the panel. The edge seals are therefore formed with a relatively constant width which gives the finished panels an excellent appearance and a high mechanical strength. Typically the width of the bonded region between the glass sheets is between 3 and 10 mm. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1a shows a detail of the edge of a panel under construction before the solder glass is melted; and Figure 1 b shows the same detail after the solder glass has been melted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The lower glass sheet 10 is slightly larger than the upper glass sheet 11 which rests on an array of support pillars 12 at a predetermined spacing above lower sheet 10. A strip of solder glass 13 is laid on the extending edge 14 by which the edge of lower sheet 10 extends beyond the edge of upper sheet 11. The solder glass is deposited either as a liquid slurry, a powder, or a rod. The strip of solder glass 13 bridges the gap 15 between the glass sheets and contacts the end edge 16 of upper glass sheet 10. When the construction is heated and the solder glass melts, it flows between the two glass sheets 10 and 11 by the action of capillary forces. The distance the solder glass flows can be controlled by varying the time and temperature of the process. In this way it is not necessary for solder glass between the two glass sheets to be expelled by the weight of the upper glass sheet. It should be appreciated that although this invention has been described with reference to a specific example it need not be limited to that embodiment. For example, one glass sheet need not be a slightly different size to the other and both sheets could be the same size provided they were translated out of registration with each other in both orthogonal directions.

Claims: A method of forming an edge seal for a thermally insulating glass panel that comprises first and second spaced apart sheets of glass [10,11] enclosing a low pressure space [30] interconnected by a glass solder edge seal [13] and an array of pillars [12], the method comprising the steps of: (a) arranging the array of pillars [12] between the first and second sheets of glass [10,11] to support and space apart the sheets of glass, and such that their edges [14,16] are not in registration, and at any point around the periphery of the panel the edge [14] of one of the sheets of glass extends beyond the edge [16] of the other; (b) after step (a), depositing a strip of solder glass around the periphery of the panel on the extending edges of the glass sheets; (c) heating the panel to melt the solder glass such that it runs between the glass sheets; and (d) cooling the panel to solidify the solder glass. A method according to claim 1, wherein the first and second glass sheets [10,11] are prepared by making one slightly smaller than the other. A method according to claim 1 or 2, wherein one glass sheet [10] overlaps the other [11] by between 1 and 10 mm. A method according to claim 3, wherein one glass sheet [10] overlaps the other [11] by about 5 mm on all sides. A method according to any one of the preceding claims, wherein the solder glass strip is deposited on the extending edges such that it bridges the gap between the sheets and contacts the end edge of the other sheet.

Inventors: COLLINS RICHARD EDWARD, TANG JIAN-ZHENG, COLLINS, RICHARD EDWARD, TANG, JIAN-ZHENG
Applicants: UNIV SYDNEY, THE UNIVERSITY OF SYDNEY
Application year: 1994
Main classification: E06B3
IPC codes: E06B3, C03C27